DONETSK, UKRAINE – Three Ukrainian helicopter gunships mounted a heavy attack on the rebel-held international airport terminal at Donetsk on Monday, firing rockets and cannon and throwing out decoy flares as militants shot at them from the ground.

The Mi-24 helicopters raked the recently built concrete-and-glass building of Sergei Prokofiev International Airport and struck targets near the runway, sending up a new plume of heavy, black smoke.

The fierce and dramatic confrontation took place just a day after Ukraine elected new President Petro Poroshenko. His election was marred immediately by scores of armed separatists who seized control of Donetsk airport on Monday, halting flights out of the rebellion-hit eastern Ukrainian city in a clear signal of defiance.

The strategic transport hub was evacuated and sealed off after gunmen claiming to be from the self-declared Donetsk People’s Republic showed up overnight demanding that Ukrainian troops guarding the airport perimeter be withdrawn.

The raid was launched in the hours after billionaire Petro Poroshenko claimed victory in a presidential election Sunday that the pro-Russian rebels have dismissed as illegitimate.

“At 3:00 in the morning, a group of armed men came. There was no shooting,” airport spokesman Dmytro Kosinov said.

The last scheduled airplane allowed to leave was the 7 a.m. flight to Kiev.

“We do not know when we will be up working again,” Kosinov said.

An AFP journalist saw three military trucks with scores of well-armed men in camouflage, some wearing pro-Russian ribbons and others with Cossack hats and beards, driving toward the airport through a traffic police checkpoint a few hundred meters from the main terminal.

Airport officials stopped media and passengers wanting to travel from getting close enough to the main entrance to see the airport buildings, but a journalist saw people walking around on the roof of the modern terminal from another location on the edge of the airport territory.

Separatists in the heavily Russified eastern rust belt of the ex-Soviet nation launched an insurgency against Kiev’s rule in early April and have seized about a dozen cities and towns in the Donetsk and Lugansk regions neighboring Russia.

The rebels thwarted voting across parts of eastern Ukraine during Sunday’s presidential election and several commanders said they did not recognize Poroshenko’s legitimacy and would continue their independence fight.

“We consider Poroshenko — if he is elected — to not be legitimate. We won’t recognize this vote,” said Oleh Tsarov, a former member of the Regions Party of toppled pro-Russian president Viktor Yanukovych.

“We consider that the winner of the election is president of west Ukraine — he is a half president,” he said as he walked through a hotel in Donetsk with armed guards.

The armed rebellion blocked voting across most of Donetsk and Lugansk, two regions that together make up around 15 percent of the national electorate.

Poroshenko has pledged to try to bring peace to Ukraine but said Monday he would press on with a military offensive against the “terrorists” in the east.

“Let the people who elected him recognize him, but for us here he won’t be our president,” said pro-Russian shopkeeper Tetyana Krasikova.

“In the east his election won’t change anything,” she said. “The people have been too humiliated, too many have died to go back to the way things were.”

Others in Donetsk threw their support behind the likely new president despite not being able to vote.

“For me it is a positive step — and not only because I like his chocolate,” said small business owner Anton Berdshadsky, 32.

“As a businessman he might be able to help create jobs and develop the economy.”

“Obviously his first challenge will be to solve the situation in the east but what can he do when the army doesn’t work and war is already here? It will be difficult to change the way people think.”